DNA Forensics

DNA Fingerprinting - What is It?

• Use of molecular genetic methods that determine the exact genotype of a DNA sample in a such a way that the results distinguish one biological organism from another

• This unique genotype = DNA Profile

It’s not that complicated• A DNA fingerprint is a method of

looking at the similarities and differences that exist in organisms’ DNA sequences

• Distinguish one biological organism from another

• Individually discriminating southern blot minisatellite hybridization profile

Collect Tissue Sample

How to do DNA FingerprintingThe Big Picture

>1000 cells

RFLP / Southern blot PCR AnalysisRFLP / Southern blot

>20 cells

DNA Fingerprinting RFLPDetermination of an individual’s unique collection of DNA restriction fragments

Collect Tissue Sample

How to do DNA FingerprintingThe Big Picture

>1000 cells

RFLP / Southern blot PCR AnalysisRFLP / Southern blot

>20 cells

Non Coding vs Coding DNA• The majority of our genome is made up non coding

DNA• How much?• Of this a large portion is of short sequences that are

repeated, sometimes hundreds of times. There are numerous forms of this "repetitive DNA"

Short Tandem Repeats(STR’s)

STR – region of DNA containing tandem copies of di-, tri- or tetranucleotide repeat units.

Examples:Dinucleotide repeats: GTGTGTGTGTGT……

Trinucleotide repeats: ACGACGACGACG……Tetranucleotide repeats:TATCTATCTATC……

More on STRs• Number of repeats varies greatly between

individuals• STRs make up 10-15% of the mammalian

genome• STRs are also called “microsatellites”

Possible Patterns for a Single “Gene” With Three Alleles

In a standard DNA fingerprint, about a dozen sites are analyzed, with each site having many possible alleles.

PCR = Polymerase Chain Reaction

What is It?• Basically DNA replication in a tube• Needs the same basic components as DNA

replication:

• DNA nucleotides, the building blocks for the new DNA • Template DNA, the DNA sequence that you want to

amplify • Primers, single-stranded DNAs between 20 and 50

nucleotides long that are complementary to a short region on either side of the template DNA

• Taq polymerase, a heat stable enzyme that drives, or catalyzes, the synthesis of new DNA

• Targets a particular sequence and amplifies it many many, many, many times

PCR https://www.youtube.com/watch?v=2KoLnIwoZKU

CODIS Loci• Combined DNA Index System• 13 Loci across human genome

Multilocus analysis - 7 loci

DNA Allele Interpretation• http://www.newscientist.com/article/mg20727733.500-fallibl

e-dna-evidence-can-mean-prison-or-freedom.html#.U0f7lsYh5W4

Grim Sleeper

MZ DZDZ

Monozygotic (Identical) and Dizygotic (Fraternal)

twins STR Analysis

Mitochondrial DNA

Y Chromosomal Inheritance

https://genographic.nationalgeographic.com

Homework

• See Blackboard for Assignments for this Special Topic